A large majority of NXT I2C sensors use address 0x02. If all the sensor ports shared the same I2C bus, you would be very limited in the number of I2C sensors you could use. Some of the analog sensors use the “I2C” pins (5 and 6) as signal pins (e.g. to control the LED on the NXT light sensor). The NXT color sensor uses a custom communication protocol (that mixes analog and digital on pins 5 and 6).

Because the bus can only be driven low, the pullups determine the bus voltage. As long as you use pullups to 3v3 (and you don’t have any other pullups on the bus to a higher voltage), it is safe to use with a 5v Arduino.

On your next trip, how about looking for non-marked knobs (no line, or any other position indicator) that fit COM-10982 (doesn’t need to be clear; preferably aluminum)? I’ve looked online for hours, and have only found ONE style of knob that isn’t marked (for $4 each).

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